I want videos on the web to have an audio-only mode

When people use video platforms to listen to music, chances are they don't look at the video, but their browser does download it. On a large scale, this probably has environmental impact: it wastes energy consumption.

What if there was a way for browsers to only stream audio, for instance when the user chooses, and automatically when the user is not looking at the tab where the video stream is happening?

Maybe it could be realized through an update to the video-element to allow for providing an audio-only source, which video platforms could then use.